Information signals, and in particular television signals, are often transmitted either via a cable connected to a set-top box, or via terrestrial broadcast received by an antenna or satellite dish. In each case, the signals are typically formed of a number of distinct information components transmitted in designated frequency channels. Such a multi-channel signal is referred to herein as a “broadcast signal.” Information in the broadcast signal may be processed by a tuner to, inter alia, extract one or more desired channels from the broadcast signal. For example, the broadcast signal may include signals across the television signal spectrum including the very high frequency (VHF) band (i.e., television carrier frequencies of 54-216 MHz) and the ultra high frequency (UHF) band (i.e., television carrier frequencies of 470-890 MHz). The broadcast signal may also include other channel frequencies outside these frequency bands (e.g., cable broadcast signals may include, in addition to the VHF and UHF bands, other designated signal carrier frequency bands).
In general, the various frequency bands comprise a number of different channels. For example, the VHF band is divided into 12 channels (channels 2-13) and the UHF band is divided into 70 channels (channels 14-83). Each channel is allocated a certain bandwidth in the broadcast spectrum depending on the standard by which the broadcast signal is transmitted. For example, the U.S. standard allocates a 6 MHz bandwidth for each channel and specifies where in that channel video and audio information components of the signal should be modulated for transmission. A tuner allows a user to select any one of the channels in the broadcast signal to be isolated from the signal and provided, for example, to a television set for viewing.
A tuner may include a pre-amplifier to control the gain of the broadcast signal provided to the various processing components of the tuner. For example, an automatic gain control (AGC) may be arranged at the front-end of the tuner to provide an adjustable gain to the broadcast signal in an effort to maintain the signal provided by the pre-amplifier at a substantially constant level. In particular, the AGC operates to keep the signal power within a dynamic range acceptable to downstream components of the tuner and to maximize signal strength while maintaining a low level of signal distortion.